CNS Flashcards
Which of the following regarding meningiomas is true?
A They show a moderate male predominance
B They grow more rapidly during pregnancy
C They are fast growing tumours
D They are common in children
B
Explanation
Meningiomas are predominantly benign tumours of adults, usually attached to the dura, that arise from the meningothelial cell of the arachnoid. They are slow growing lesions. They are uncommon in children and generally show a female predominance (3:2). Meningiomas often express progesterone receptors and may grow more rapidly during pregnancy
Which of the following regarding multiple sclerosis (MS) is incorrect?
A The frequency of relapses tends to decrease during the course of time
B Women are affected twice as often as men
C MS is a demyelinating grey matter disease of the brain
D IgG levels in the CSF are raised
C
Explanation
MS is an autoimmune demyelinating disorder characterised by distinct episodes of neurological deficits, separated in time, attributable to white matter lesions that are separated in space. It is the most common of the demyelinating disorders. Women are affected twice as often as men. The disease may become apparent at any age but the onset in children or after the age of 50yr is rare. The frequency of relapses tend to decrease during the course of time, but there are steady neurologic deterioration in most affected individuals. Examination of the CSF reveals a mildly elevated protein level and in one third of cases there is moderate pleocytosis. IgG levels are increased and oligoclonal bands are usually observed on immunoelectrophoresis.
Morphology (grey areas of discolouration):
- active plaques represent myelin breakdown
- inactive plaques represent gliosis
Clinical features:
- unilateral vision impairment (optic neuritis)
- brainstem: CN, ataxia, nystagmus, internuclear ophthalmoplegia
- spinal cord lesions: motor/sensory impairment, bladder dysfunction
CNS rabies, which is incorrect?
A Is only transmitted to humans through a bite
B The incubation period depends on the distance between the wound and the brain
C Local paraesthesia around the wound plus systemic symptoms is diagnostic
D Negri bodies are pathognomonic of rabies
A
Explanation
Rabies is a severe encephalitis transmitted to humans by the bite of a rabid animal-usually a dog or various wild animals. Exposure to certain species of bats, even without a known bite, can also lead to rabies. Negri bodies, the pathognomonic microscopic finding, are cytoplasmic, round to oval, eosinophilic inclusions that can be found in pyramidal neurons of the hippocampus and Purkinje cells of the cerebellum, sites usually devoid of inflammation. Since the virus enters the CNS by ascending along the peripheral nerves from the wound site, the incubation period (1-3months) depends on the distance between the wound and the brain. The disease begins with non specific symptoms of malaise, headache, and fever, but the conjunction of these symptoms with local paraesthesia around the wound is diagnostic. As the infection advances, the slightest touch is painful, with violent motor responses progressing to convulsion. Contracture of the pharyngeal musculature may create an aversion to swallowing event water (hydrophobia). Periods of mania and stupor progress to coma and eventually death, typically from resp failure.
Extra:
Rabies is transmitted to humans by the bite of a rabid animal, a dog or various wild animals that form natural reservoirs. Exposure to bats , even without a known bite, has also been identified as a risk factor for developing infection, although transmission appears to be limited to certain bat species.
Rabies can be transmitted through contact with the saliva of an infected animal. Bites are the most common mode of rabies transmission but the virus can be transmitted when saliva enters any open wounds or mucus membranes (such as the mouth, nose or eye)
Source: www.iamat.org
Regarding cerebrospinal fluid, which is correct?
A The osmolality of CSF is the same as plasma
B Turnover of CSF occurs 6 times a day
C Absorption of CSF occurs in choroid plexus
D 350mls of CSF is produced a day
A
Explanation
Cerebrospinal fluid volume in humans is 150mls and the rate of production is about 550ml/day. Thus the CSF turnover is 3.7 times a day. 50-70% of CSF is formed in the choroid plexuses and the remainder is formed around blood vessels and along ventricular walls. It is absorbed through the arachnoid villi into veins, mainly the cerebral venous sinus. The composition of CSF: it contains electrolytes (Na, K, Mg, Ca, Cl, HCO3), pco2, pH, proteins, glucose, urea, creatinine, uric acid, cholesterol, and inorganic P. Osmolality of CSF and plasma is the same= 289 mosm/kg H20. The composition of CSF is essentially the same as brain ECF, which in humans makes up 15% of the brain volume.
In which part of the CNS does polio not affect?
A Cranial motor nuclei
B Anterior horn of the spinal cord
C Dorsal root ganglion
D Posterior horn of the spinal cord
C
Explanation
Polio invades the CNS and replicates in the motor neurons of the spinal cord and brainstem. Commonly the anterior horn motor neurons of the spinal cord are involved. The posterior horns of the spinal cord and the cranial motor nuclei are sometimes involved.
It does not involve the dorsal root ganglion = Trunk ganglion which is located adjacent to the spine on a dorsal root and contains the cell bodies of afferent sensory nerves.
Extra: Robbin’s
Poliovirus is an enterovirus that most often causes a subclinical or mild gastroenteritis; in a small fraction of cases, it secondarily invades the nervous system and damages motor neurons in the spinal cord and brain stem (paralytic poliomyelitis). With loss of motor neurons, it produces a flaccid paralysis with muscle wasting and hyporeflexia in the corresponding region of the body. In the acute disease, death can occur from paralysis of respiratory muscles.
Long after the infection has resolved, typically 25 to 35 years after the initial illness, a post polio syndrome of progressive weakness associated with decreased muscle bulk and
pain can appear. The cause of this syndrome is unclear. One hypothesis is that motor neurons that survive the initial insult sprout new nerve terminals to compensate for the death of their neighbors, and that over time the additional demands placed on these neurons leads to injury that diminishes function or causes cell death.
Which is FALSE regarding atraumatic intracerebral haemorrhage?
A Cerebral amyloid angiopathy bleeds are often restricted to the leptomenigeal and cerebral cortical arterioles
B Peak incidence is 60yrs of age
C Hypertensive haemorrhages occurs most often in the putamen region
D The two main aetiologies are hypertension and congenital aneurysms
D
Explanation
Atraumatic intracerebral haemorrhage occurs in middle to late adult life. Peak incidence 60yrs. The 2 main aetiologies are hypertension and cerebral amyloid angiopathy (CAA). Other local or systemic factors may cause or contribute: coagulation disorders, neoplasms, vaculitis, aneurysms and vascular malformations. Hypertension accounts of >50% of clinically significant haemorrhages and for 15% of deaths in patients with chronic hypertension. These haemorrhages occur in the putamen (50-60%), thalamus, pons and cerebellar hemispheres. CAA bleeds are often restricted to the leptomenigeal and cerebral cortical arterioles and capillaries
Which is true regarding a retinoblastoma?
A The cellualr origin of retinoblastoma is a neuronal cell
B Metastasis occur to the brain and often to the lungs
C Retinoblastoma is the second most common malignancy in children
D Surgery is the first option of treatment
A
Explanation
Retinoblastoma is the most common primary intraocular malignancy of children. The molecular genetics of retinoblastoma indicate that the cell of origin is neuronal. Approximately 40% of cases occur in patients who inherit a germline mutation of one RB allele, therefore heritable. Remaining 60% of the tumors develop sporadically (these have somatic RB1 gene mutation).
Morphology:
- nodular mass in the posterior retina, often with satellite seedings
- on light microscopic examination: undifferentiated areas of the tumor found to be composed of small, round cells with large hyperchromatic nuclei & scant cytoplasm, resembling undifferentiated retinoblast
- differentiated structures: characteristics of Flexner-Wintersteiner rosettes (clusters of cuboidal/short columnar cells arranged around a central lumen)
Clinical features:
- median age at presentation is 2years (may present at birth)
- poor vision, strabismus, whitish hue to the pupil “cat’s eye reflex”, pain and tenderness in the eye
Fatal if untreated
Tx: enucleation, CTx, RTx
Chemotherapy is often the first of treatment to attempt to reduce the tumour followed by laser treatment or cryopexy.
Spread is to the brain and bone marrow and seldom to the lungs (osteosarcoma/ soft tissue tumors)
Prognosis is poor if there is extra ocular extension and invasion along the optic nerve, and by choroidal invasion.
Which metabolite accumulates in stroke propagating cellular damage?
A Glutamate
B Glycine
C Lactate
D GABA
A
Explanation
Ischemia leads in ATP depletion in stroke by multiple mechanisms. One of which includes inappropriate release of excitatory amino acid neurotransmitters (e.g. glutamate) that cause cell damage via calcium influx through NMDA-type glutamate receptors.
A 70-year-old man with longstanding hypertension develops an acute intra-cranial haemorrhage. What is the most likely site?
A Frontal lobe
B Thalamus
C Putamen
D Temporal lobe
C
Explanation
Hypertensive intracerebral haemorrhages most commonly occur in the putamen (50-60%), thalamus, pons, and cerebellar hemispheres (rarely)
What is the first pathological change seen with primary angle closure glaucoma?
A Transient iris apposition to lens
B Increased pressure in anterior chamber
C Increased pressure in posterior chamber
D Occlusion of trabecular meshwork
A
Explanation
Primary angle-closure glaucoma occurs in anatomically predisposed eyes by transient iris apposition to the lens blocking aqueous humour passage from the posterior to anterior chambers. Pressure builds in the posterior chamber bowing the iris forward and occluding the trabecular meshwork.
Extra: Primary angle closure glaucoma occurs in hyperopics with shallow anterior chambers - transient apposition of the pupillary margin of the iris to the anterior surface of the lens may results in obstruction to the flow of aqeous humour through the pupillary aperture. The posterior chamber pressure rises as aqueous humour production continues, which may then bow the iris forward and appose it to the trabecular meshwork. Whereas in secondary angle-closure glaucoma there is contraction of various pathologic membranes that form over the surface of the iris and draw the iris over the trabecular meshwork occluding aqueous outflow. I would have thought therefore that the most correct answer for the first pathological change seen in Primary Angle-Closure Glaucoma would be transient apposition of the iris to the lens, whereas in secondary angle-closure it would be trabecular meshwork occlusion.
What is the most common brain tumour in childhood?
A Lymphoma
B Astrocytoma
C Medulloblastoma
D Meningioma
B
Explanation
The current TB does not clearly state a most common brain tumour of childhood. The most common poorly differentiated neoplasm is medulloblastoma – which accounts for 20% of brain tumours in children. Meningiomas are predominantly benign tumours of adults. Gliomas are the most common group of primary brain tumours (which includes astrocytomas, oligodendrogliomas, ependymomas).
“Neoplasms that exhibit sharp peaks in incidence in children younger than age 10 years include (1) leukaemia, (2) neuroblastoma, (3) Wilms tumour, (4) hepatoblastoma, (5) retinoblastoma, (6) rhabdomyosarcoma, (7) teratoma, (8) Ewing sarcoma, (9) juvenile astrocytoma, (10) medulloblastoma, (11) ependymoma
An internet search “Pilocytic astrocytoma (Grade 1): This slow-growing tumor is the most common brain tumor found in children”
Uptodate: Paediatric primary brain and CNS tumours: distribution by tumour type:
Pilocytic astrocytoma-15.5%
Gliomas-11.7%
Embryonal-11.4% (medulloblastoma 63.7% in the group)
Meningioma-2.6%
Lymphoma-0.3%
Source: Uptodate: Epidemiology of central nervous system tumours.
